The present invention relates to an automatic transmission.
Recently, an automatic transmission that is installed in a vehicle is required to have a plurality of speeds, such as eight forward speeds, for example. The automatic transmission is also required to have its structural parts, such as clutches, for example, arranged such that the automatic transmission will be compact, making it easier to install.
There exists an automatic transmission (see, for example, Japanese Patent Application Publication No. JP-A-7-269665) that attempts to achieve a compact structure, in particular, compactness in the axial direction, by arranging two clutches such that they overlap in the axial direction and are positioned differently in the radial direction. In the two clutches, either the input or output member is provided as a common member, and the other is provided as a separate member. In each of the two clutches, a plurality of friction plates, a working fluid chamber that operates the friction plates, and a cancel oil chamber that cancels centrifugal oil pressure the working fluid chamber, are disposed such that they overlap in the axial direction.
The two working fluid chambers and cancel oil chambers are disposed in a clutch drum that forms a single unit with a turbine shaft. Hydraulic pressure is supplied to the two working fluid chambers through an oil passage that is formed in a boss portion of the clutch drum. One of the two cancel oil chambers that is located to the inside in the radial direction is directly supplied with oil through an oil hole that is formed in the boss portion of the clutch drum. The oil from the cancel oil chamber to the inside in the radial direction is supplied to the other of the two cancel oil chambers, which is located to the outside in the radial direction, through an oil passage that is provided in a piston for a clutch to the inside in the radial direction and through the oil passage that is formed in the boss portion of the clutch drum to the inside in the radial direction, which is a securing member.